This invention relates to the production of partially oriented yarns from polyesters, specifically polytrimethylene terephthalate. More specifically, the present invention is a spin draw process for making partially oriented yarn from polytrimethylene terephthalate.
Partially oriented yarn (POY) is filament yarn in which the draw ratio is less than normal, i.e., less than that used to make fully oriented yarn (FOY), resulting in only partial longitudinal orientation of the polymer molecules. This necessary orientation can be created by normal drawing between godets or just by adjusting the speed of the first godet pair relative to that of the spinneret. Generally, in making POY from polyesters, especially polyethylene terephthalate (PET), the extruded or formed yarn goes through a free drop from a spinneret to a winder. This is the most economical process and it works well for PET because PET has a wide processing window, i.e., a winding speed of from 50 to 10,000 meters per minute. This type of process does not work well for polytrimethylene terephthalate (PTT) because it has a much narrower processing window, i.e., 500 to 4000 meters per minute. If the speed is higher than this, then the Tg of the polymer increases. This makes it hard to establish stable conditions during the drawing process because the yarn is so sensitive to tension when it is formed from PTT.
Spin draw processes are generally used to make FOY. They generally comprise two or three pairs of godets which are generally heated to various degrees and between which the drawing of the yarn takes place. This type of process is not used to make POY because it is more expensive than the process described in the preceding paragraph.
This invention is a spin draw process for making partially oriented yarn from polytrimethylene terephthalate (PTT) which comprises the steps of:
(a) extruding and spinning PTT and forming a monofilament or multifilament yarn therefrom,
(b) heating the yarn by contacting it with a first pair of godets (G1), moving at 1800, preferably 2000, to 3500 meters per minute at a temperature to give a yarn temperature of PTT above the glass transition temperature (Tg) and less than the cold crystallization temperature, (Tcc) of the PTT yarn.
(c) moving the yarn between the first godet pair and a second pair of godets (G2) moving at 1250, preferably 2450, most preferably 2560, to 4550 meters per minute and which is set at a temperature to give a yarn temperature of PTT of 45, preferably 60, to 120xc2x0 C., preferably 100xc2x0 C., most preferably less than 100xc2x0 C., at a draw ratio (the ratio of speed of second godet pair to first godet pair (G2/G1) of 0.7 to 1.3, preferably less than 1.3, most preferably 0.95 to 1.28, and
(d) winding the yarns at the speed of 1 to 15% less than that of the second godet pair (or third godet pairxe2x80x94G3) and at temperature less than the glass transition temperature of PTT yarn.
The process may be operated wherein the first pair of godets is moving at greater than 3500 meters per minute. Then the speed of the second pair of godets is from 2450, preferably 2560, to 10,000 meters per minute and the temperature of the second pair of godets should be set to give a yarn temperature of PTT from 80 to 180xc2x0 C. and the draw ratio should be 0.7 to 3.0, preferably 0.7 to less than 3.0, most preferably 0.95 to 2.0.
The other desirable process utilizes three pairs of godets. The first set of godets is at room temperature. A small draw or no draw is achieved between the first two sets of godets. The second is heated and a major draw may occur between the second and the third pair of godets (G3). The third pair is also heated to stabilize the final POY package.
A spin draw process is described herein for making POY from PTT. POY with a range of elongation and tenacity can be produced by varying spinning and drawing conditions (speeds, temperature, etc.). The purpose of using a spin draw machine to make PTT POY is to stabilize the fiber against shrinkage and to improve package stability and shelf life by developing a sufficiently high crystallinity and relax the stress built during drawing between godets using heated godets prior to winding.
The drawing process generally involves two or more pairs of godets. For example, Barmag, Toray, Murata, Zimmer, and Teijin Seiki spin draw machines may be used in making PTT POY. In this process a first pair of take-up godets (G1) is used to heat the yarn to a yarn temperature above the glass transition temperature (Tg) of PTT, generally greater than 45xc2x0 C., but lower than the cold crystallization temperature, Tcc, of PTT (generally less than 60 to 65xc2x0 C.) such that the fiber can be drawn between the first pair (G1) and a second pair of godets (G2). The precise temperature for pair (G1) will depend on the machine used and is determined by the speed and diameter of the godet and the number of wraps on the godet. The second pair of godets (G2) should be at a higher temperature than that of the first set of godets (G1), preferably to give a yarn temperature of 80 to 90xc2x0 C. Again, the precise temperatures will depend on the speed and the diameter of the godets and the number of wraps on the godets. The yarn moves from the second pair of godets (G2) to the winder. The relative speeds of the godets and winder are:
(G1) less than, equal to, or greater than (G2) greater than or equal to Winder
A preferred process for carrying out the invention utilizes three pairs of godets. The first pair of godets (G1) is at room temperature, the second (G2) is heated and achieves a small draw, or no draw, and the third (G3) puts the majority of the draw (if there is to be any drawing at all between the godet pairs) into the yarn with drawing between the second (G2) and third godet pair (G3). This third godet pair (G3) is heated to stabilize the final POY package. In this case, the relative speeds of godets and winder are:
(G1) less than or equal to (G2) less than, equal to, or greater than (G3) greater than or equal to Winder In this situation where there is to be no draw, the draw ratio between the first two pairs of godets (the ratio of speed of the second godet pair to the first godet pair) should be from 0.3, preferably 0.7, most preferably 0.95, to 1.0 and the temperature of the second pair of godets should be set to give a yarn temperature of PTT above the glass transition temperature (Tg) and below the cold crystallization temperature (Tcc) of PTT yarn. If a small draw between the first two pairs of godets is desired, then the draw ratio may be increased up to 1.05. The draw ratio between the second and third pair of godets should be from 0.7 to 1.3, preferably 0.95 to 1.28, and the temperature of the third pair of godets should be set to give a yarn temperature of PTT the same as the temperature of second pair of godets in the previous embodiment depending upon the speed of the godets as discussed above.
Tg and Tcc can be measured with a differential calorimeter (DSC). The procedure normally used with DSC is heating the yarn at 20xc2x0 C./min. and making a temperature scan from xe2x88x9250xc2x0 C. to about 260xc2x0 C. The change in endothermic or exothermic response of the yarn is recorded. Tg is the temperature at which the yarn begins to the endothermic change from glassy state to rubbery state (observed by the deflection of the line from the temperature scan of the calorimeter). Tcc is the temperature when the exothermic change from the supercooling of the yarn due to cold crystallization becomes maximal (i.e., at the peak of the scan.) The yarn specimen for testing can be obtained from the yarns produced with the speed of the first set of godet pair set at the desired speed and the yarns wound on the first set of godet pair.
In another embodiment, the godet pairs used in this invention can be a godet and a follower instead of two godets. Oil mist would be used for slow speed and air bearing for speeds greater than 2000 meters per minute.
When the speed of the first pair of godets (or the second pair in the embodiment where three pairs of godets are used) is 1800, preferably 2000, to 3500 meters per minute, the draw ratio should be from 0.7 to 1.3, preferably less than 1.3, most preferably 0.95 to 1.28, because sufficient bulk (or crimp) can be generated using a draw texturing machine or any other type. This necessary orientation can be created by normal drawing between godets or just by adjusting the speed of the first godet pair relative to that of the spinneret. The temperature of the first pair of godets is set to give a yarn temperature of PTT above the glass transition temperature, 45xc2x0 C. plus or minus 5 to 10xc2x0 C., and below the cold crystallization temperature, 60-65xc2x0 C. The speed of the second pair of godets is 1250, preferably 2450, most preferably 2560, to 4550 meters per minute and the temperature of the second pair of godets is set to give a yarn temperature of PTT from 45, preferably 60, to 120xc2x0 C., preferably 100xc2x0 C. and most preferably less than 100xc2x0 C. This produces a yarn with an elongation of greater than 60 percent and a tenacity of less than 3.0 g/d.
When the speed of the first pair of godets is greater than 3500 meters per minute, then the draw ratio should be from 0.7 to 3.0, preferably less than 3.0, most preferably 0.95 to 2.0. The temperature of the first pair of godets is the same as above but the temperature of the second pair of godets is set to give a yarn temperature of PTT ranges from 80 to 180xc2x0 C. The speed of the second pair of godets is 2450, preferably 2560, to 10,000 meters per minute. This produces a yarn with an elongation of greater than 20 percent and a tenacity of less than 5.0 g/d.
An example of typical operating conditions is shown below:
The speed (draw) ratio is speed of 2nd godet pair /speed of 1st godet pair=1.2-1.7 and speed of 2nd godet pair/speed of winder=1.01-1.10.
The key points in selecting the exact conditions to use on a particular machine and with a particular yarn are as follows. The temperature of the first pair of godets must be set to give a yarn temperature of PTT lower than the cold crystallization temperature of Tcc and greater than its glass transition temperature, Tg. The temperature of the first pair of godets is chosen depending on the diameter of the godet, the number of wraps, and the speed of the godet pair. The draw point of the filaments is controlled at the point of the last wrap just before leaving any godet pair. The speed of godet pair is chosen such that the yarn wraps are stable. The temperature of the next pair of godets develops the yarn morphology and stress relaxation such that it is stable against shrinkage. It also controls the yarn boiling water shrinkage. The relative speeds of the godet pairs, i.e., the draw ratio, control the elongation and the tenacity of the filaments.
The primary purpose of the process of the present invention is to prevent shrinkage of the POY package during winding and a stable package for long shelf life.